Table 2.

Description of statistical models

Methods section	Statistical model
2.5.1 DHEA & Cortico-Hippocampal Structural Covariance	(1)Whole-brain CTh = 1 + DHEA*Hippocampus + DHEA +Hippocampus + Collection Time + Age + Sex + Scanner + Handedness + Total Brain Volume + random (id) + I (2)Whole-brain CTh = 1 + DHEA*Hippocampus*Sex + DHEA*Hippocampus + Hippocampus*Sex + DHEA*Sex + DHEA +Hippocampus + Sex + Collection Time + Age + Scanner + Handedness + Total Brain Volume + random (id) + I (3)Whole-brain CTh = 1 + DHEA*Hippocampus*Age + DHEA*Hippocampus + Hippocampus*Age + DHEA*Age + DHEA +Hippocampus + Age + Collection Time + Sex + Scanner + Handedness + Total Brain Volume + random (id) + I (4)Note that in order to limit the number of control variables per model: models (1), (2), (3) and (4) were retested while adding testosterone, estradiol, pubertal stage or season of sampling as additional covariates (one at a time)
2.5.2 Cortico-Hippocampal Structural Covariance & Cognitive Tests	(1)Following significant results with the ‘DHEA*Hippocampus’ term in section 2.5.2: Cognitive Scores = 1 + CTh*Hippocampus + CTh + Hippocampus + Sex + Age + Scanner + Handedness + Total Brain Volume + random (id) + I
2.5.3 Mediation	(1)Beta coefficients and p-values extracted from section 2.5.1 (2)Beta coefficients and p-values extracted from section 2.5.2 (3)Beta coefficients and p-values from (1), (2) and (3) were extracted from existing analyses, and entered in the Sobel-Goodman test calculator to formally test mediation effects of scans per participant (see ‘Methods’)

The specific statistical term of interest is underlined in each model; the rest of the terms represent control variables.

‘id’ refers to a specific participant’s identification number: this term is included in order to identify and link all longitudinal data from the same participant

‘I’ to the identity matrix of the mixed effects model

‘CTh’ in section 2.5.2 refers to average cortical thickness of the brain regions found to be significant in section 2.5.1